"If you think showing me a text will thaw me out, think again. Only a coat could do that."

TOMORROW, my younger sister and I will travel to Notre Dame University for my son’s graduation. But today, we’re on the train, heading towards Hotel Lincoln, Old Town Chicago, and my sister’s tapping in unnerving fashion on her iPad, giving me a beady look from time to time. Not quite the stink-eye but almost.

I know what the look is about; this is the thing about sisters — you understand every single thing they’re not saying, which can be something of a mixed blessing, for what she’s not saying right now is this: I love you. But I know the sort of person you are. Oh Christ, how I know you.

I cannot argue with her; it’s hard to argue this point with someone who’s shared a bedroom with you for years and seen you pee in the bedroom sink at two in the morning, even if it was only once. And who knows, what’s more, that the reason you did this was because you were too lazy to walk down the corridor, take a right, and pee in the toilet like any normal 12-year-old would do.

I mean let’s be honest, that’s what you call knowing someone.

And now she’s giving me another look, which says: so, in light of the fact that I know you as I do — how on earth was I stupid enough to trust you when you said you’d researched the weather in Chicago and told me not to bring my coat?

There’s not much I can say in my defence when outside it is sleeting. How can I muster indignance when my sister’s feet are going blue in their flip-flops and I’m wearing what feels like a hankie. When hypothermia has frozen my tongue, and every other passenger is looking at us from inside their cosy puffa-jacket cocoons as if at idiots abroad, which I fear we are.

I tell my sister yet again about the text my son sent me a few days before our departure — 28 degrees, Mum. Swimming in Lake Michigan. Class! — and explain how I felt this obviated the need to conduct any further meteorological research but she simply gives me another look. This one says, “I am used to being prepared for every eventuality — as befits someone whose job entails making life-and-death decisions on a daily basis. And you are unused to it, as befits someone whose job does not. HOW COULD I HAVE FORGOTTEN THIS IMPORTANT FACT?”

“That’s as maybe,” I think, “but in my mind’s eye, I can see you aged seven, getting up to your infernally neurotic doomsday-planning tricks. On a nightly basis. Sharing a bedroom works both ways, sista.”

Perhaps, I think, I should show her my son’s text, but just when I’m stabbing at my phone with frozen-sausage fingers, so as to find it in my inbox, she gives me a look — the beadiest yet by far — which says, “if you think showing me that text is going to thaw me out, think again.

Only a coat could do that,” so I decide against it, stuff my frozen sausages back inside my hankie garb and look out of the window at the sleet instead.

Secretly, I’m relieved; America doesn’t seem to suit my Nokia brick; the chances of finding that text were slim, for my phone’s had no signal since we arrived and I cannot for the life of me work out why. But I daren’t tell my sister because it has the address of the Hotel Lincoln on it. My sister delegated the Hotel Lincoln leg of our journey to me and I’ve had quite enough looks for one day.

“It is four degrees in Chicago,” my sister announces suddenly, looking up from her iPad. It’s as I feared; she’s been looking up weather websites. “And AccuWeather Forecast for Illinois says it is going to dip to minus one tonight.”

Then she says, “so what’s the plan when we get to the hotel, besides ordering extra blankets?”

I look at her, and think, “Lucky for you I haven’t forgotten that you never did tell Dad why the bedroom sink suddenly came away from the wall.”

“Well?” she says. “What’s the plan?”

“I dunno, you bloody head-case,” I say. “How about a swim in the lake?”